This invention relates in general to making thin strip and more particularly casting of thin strip by a twin roll caster.
It is known to cast metal strip by continuous casting in a twin roll caster. Molten metal is introduced between a pair of counter-rotating horizontal casting rolls which are cooled so that metal shells solidify on the moving roll surfaces, and are brought together at the nip between them to produce a solidified strip product delivered downwardly from the nip between the rolls. The term “nip” is used herein to refer to the general region at which the rolls are closest together. The molten metal may be poured from a ladle into a smaller vessel or tundish/distributor, from which it flows through a metal delivery nozzle located above the nip, which directs the molten metal to form a casting pool supported on the casting surfaces of the rolls above the nip. This casting pool is typically confined at the ends of the casting rolls by side plates or dams held in sliding engagement adjacent the ends of the casting rolls.
In casting thin strip by twin roll casting, a brush is provided to clean debris from each of the casting rolls, such as accumulation of metal oxides and slags or other contaminants on the roll surfaces. During casting the surfaces of the casting rolls are continuously cleaned ahead of contacting the molten metal in the casting pool.
For example Japanese Patent Publication JP 3230849-A by Nippon Steel Corporation and Mitsubishi Heavy Industries KK discloses two sets of divided roller brushes applied to the surfaces of chilled casting rolls with the brushes of one set being staggered with respect to those of the other set to provide brushing action across the complete width of the casting roll. Japanese Patent Publication JP 01083341-A also by Nippon Steel Corporation and Mitsubishi Heavy Industries KK also discloses a twin roll caster in which the casting rolls are cleaned by brushes. Further, Japanese Patent Applications 29393/97 and 29394/97 for Nippon Steel Corporation disclose roll cleaning arrangements in which two cylindrical cleaning brushes are brought successively into contact with a casting roll at different stages of a casting run. Additionally, U.S. Pat. No. 4,793,400 discloses a casting drum cleaner in which a pair of similar rotating brushes are applied in tandem to the drum, both brushes being driven in opposite directions to the rotation of the drum. Other roll brushing arrangements are disclosed in our U.S. Pat. Nos. 5,307,861 and 5,575,327.
Previously, various designs have been proposed for cleaning brushes, with a variety of bristle patterns. Examples of cleaning brushes are disclosed in Japanese Patent Publication No. JP 03-118944 and European Patent No. 0461898.
The present invention provides an improved apparatus for casting metal strip and method of continuously casting metal strip. Disclosed is a method for casting metal strip comprising:                (a) assembling a pair of casting rolls laterally disposed to form a nip between them,        (b) assembling a pair of brush rolls with one of each of the brush rolls associated with one of each of the casting rolls, each brush roll including at least one spaced apart brush line extending substantially along the axial length of the casting roll,        (c) introducing molten metal to form a casting pool of molten metal supported on the casting rolls above the nip, and        (d) counter rotating the casting rolls to deliver cast strip downwardly from the nip and rotating the brush rolls to clean the casting rolls.        
The brush roll may include one or more brush lines. Each brush line may form a spiral array along the brush roll. Alternatively, the brush lines may form other desired geometric arrays such as zigzags, waves, and crisscrosses. In any case, the brush lines may be 10 mm to 50 mm apart separated by open space of 2 mm to 45 mm. The brush lines may set at one line per 10 mm to 90 mm of axial length of brush roll.
The brush roll may include one or more rings including spaced apart bristles to form the brush lines. The bristles may be regularly or irregularly spaced apart in the rings. The brush roll may include a plurality of rings staggered about the brush roll.
Various aspects of the invention will be apparent from the following detailed description, drawings, and claims.